A vacuum jacketed pipeline is taught by U.S. Pat. No. 3,360,001 dated Dec. 26, 1967 and issued to J. H. Anderson on a Vacuum Jacketed Pipeline And Joint Construction Therefor. A similar pipeline with insulation in the annular space between the jacket and inner conduit is taught by U.S. Pat. No. 4,219,224 dated Aug. 26, 1980 and issued to B. C. Hanley on a Cryogenic Pipeline System. Each of said patents recognizes the problem of a heat leak path between the jacket and the inner conduit. Each patent solves the problem by using low heat conducting material extending between the jacket and the inner conduit. Even with low heat conducting materials, there still remains a direct conductive heat leak path.
The present invention solves the problem of minimizing heat leak between the inner conduit and jacket at the joint while providing a spool member capable of being vacuum tested at the factory for leaks after bake-out of the annular space between the inner conduit and the jacket, while at the same time providing a spool member which will not have a direct conductive heat leak path between the jacket and the inner conduit when installed.